This invention relates to the production of heavy paraffins from synthesis gas in a Fischer-Tropsch reactor using a supported cobalt catalyst. The synthesis gas is produced by partial oxidation of a light hydrocarbon stream in an autothermal reactor wherein the reactant streams to the autothermal reactor are charged to the autothermal reactor at a pressure sufficient to supply process pressure for the entire synthesis gas production process and the Fischer-Tropsch synthesis process.
Fischer-Tropsch processes are well known for use in converting synthesis gas, i.e., a mixture of carbon monoxide and hydrogen, into higher hydrocarbon products. Processes for the production of lighter fuels, such as jet fuel, diesel fuel, gasoline and the like are well known as are processes for the production of heavier paraffins. A variety of catalysts are used in such processes. Particularly, supported iron catalysts have been used for the production of light hydrocarbon fuels. More recently, supported cobalt catalysts have been used to produce liquid paraffins from synthesis gas in Fischer-Tropsch processes.
A continuing problem with Fischer-Tropsch processes is the production of the liquid hydrocarbon fuels at a competitive price. Accordingly, a continuing effort has been directed to the development of more economical methods for producing hydrocarbon fuels by Fischer-Tropsch processes.
In recent years, slurry bubble column reactors which utilize finely divided catalyst which is frequently cobalt, ruthenium or combinations thereof supported on an inorganic oxide such as alumina, titania, silica, silica alumina or the like have been utilized. The catalyst in such processes is finely divided and is maintained in suspension in a slurry comprising a liquid comprising reaction products, the finely divided catalyst particles and gas bubbles comprising synthesis gas by upward movement of synthesis gas bubbles and optimally recycle liquid into or through the slurry.
In all such processes, it is necessary that the synthesis gas be produced from some hydrocarbon fuel. Synthesis gas has been produced in the past from fuels as varied as coal, residual oils, and light hydrocarbon streams such as natural gas and other light hydrocarbons as heavy as benzene.
Commonly, the synthesis gas is produced from methane or natural gas by processes such as steam reforming or the use of autothermal reactors. Autothermal reactors typically have used a burner wherein the light hydrocarbon stream is partially combusted using air or oxygen-enriched air in combination with steam. The steam has been required to prevent the formation of soot and the like. The partially oxidized light hydrocarbon stream is then passed through a reforming catalyst bed, which may comprise nickel on alumina, where it reaches equilibrium to produce a synthesis gas mixture comprising carbon monoxide and hydrogen. Such processes are considered to be well known to those skilled in the art.
In a series of papers, xe2x80x9cProduction of Diesel Oil and Wax by Fischer-Tropsch-Synthesis using a Nitrogen-Rich Synthesis Gas-Investigations on a Semi-Technical Scale,xe2x80x9d by A. Jess, R. Popp and K. Hedden, 113, Jahrgang, Heft 12, December 1997; xe2x80x9cKinetics of the Fischer-Tropsch-Synthesis using A Nitrogen-Rich Synthesis Gas,xe2x80x9d by T. Kuntze, K. Hedden and A. Jess, OIL GASxe2x80x94European Magazine January 1995; xe2x80x9cProduction of Synthesis Gas by Catalytic Partial Oxidation of Methane with Air,xe2x80x9d by A. Jess and K. Hedden, OIL GASxe2x80x94European Magazine April 1994; xe2x80x9cA New Concept for the Production of Liquid Hydrocarbons from Natural Gas in Remote Areas,xe2x80x9d by K. Hedden, A. Jess and T. Kuntze, OIL GASxe2x80x94European Magazine March 1994; and, in a dissertation entitled xe2x80x9cSynthesis Gas Production Via Catalytic Partial Oxidation of Methane with Airxe2x80x9d presented Jun. 29, 1991, by Andreas Jess, a study of Fischer-Tropsch processes is presented. In this study, various methods for producing synthesis gas are discussed. The autothermal reactor is operated at an elevated pressure. The resulting synthesis gas is passed without the removal of water, ammonia, or other contaminants to a Fischer-Tropsch reactor in which it is reacted to produce fuels in the presence of an alkalized iron catalyst bed. Water is removed from the gaseous stream discharged from the Fischer-Tropsch reactor prior to charging the stream to a second Fischer-Tropsch reactor. These references disclose that the synthesis gas may be reacted in the Fischer-Tropsch reactor without further compression and have assumed that natural gas will be available at elevated pressure as a feed stream to the process.
Cobalt on a suitable support and in finely divided form has been used recently in slurry bubble column reactors to produce heavy paraffins. Such reactors tend to operate at higher pressures than the alkalized iron catalyst bed reactors used in the reference to produce light fuels such as, jet fuel, gasoline, diesel fuel, and the like. It is also desirable in such processes that, contrary to the references, the water resulting from the synthesis gas production be removed from the synthesis gas prior to charging it to the Fischer-Tropsch reactor.
Accordingly, a continuing search has been directed to the development of an improved method for producing heavy paraffins from a synthesis gas in a Fischer-Tropsch process using a supported cobalt catalyst wherein the process is pressurized by compressing a single reactant stream.
A method is provided for producing a synthesis gas from a light hydrocarbon stream using air or oxygen-enriched air as an oxidant in a high pressure autothermal reactor and converting the synthesis gas in a Fischer-Tropsch process using a supported cobalt catalyst to produce heavy paraffins wherein the required process pressure is supplied by charging the reactant streams to the autothermal reactor at a high pressure.